The Boy raised by The Demon Queen and The Dragon Queen has no rival

Story:

A boy named Ruisha is trapped in a distorted space created by the ancient hero. What he finds there is the Demon King and the Dragon King, who should have been defeated by the hero 300 years ago. Ruisha befriends the Demon King and the Dragon King, and is trained by them, going from a weak child to a legendary warrior with the power of both demons and dragons. Using his power, Ruisha escaped from the strange place and was accepted into the magic academy where the hero’s descendants live. And now he will have to face many challenges to free the Demon King and Dragon King.